1. Field of the Invention
The present invention relates to an internal power supply circuit for use in a semiconductor device, and more particular y to an internal power supply circuit which maintains an internal power supply voltage at a constant level.
2. Description of the Related Art
High density semiconductor memory devices often require an internal supply voltage of, for example, about 3 volts, which must be kept constant regardless of the external power supply voltage, which can have an operational range of 3.about.6 volts.
As shown in FIG. 1, a conventional internal power supply circuit includes a comparator 20 and a driver 40. The comparator 20 compares the internal voltage VCCint with a reference voltage Vref and generates a comparison result signal S.sub.-- COMP through an output node 2. The internal voltage VCCint is provided to the internal circuits of the semiconductor device through an output node 1 of the internal power supply circuit. The driver 40 is comprised of a P-channel transistor having a gate for receiving the comparison result signal S.sub.-- COMP, drain connected with the output node 1, and a source for receiving a power source voltage VCCext (hereinafter, referred to as the "external voltage") which is applied externally through an input node 3.
If the reference voltage Vref is higher than the internal voltage VCCint, the signal S.sub.-- COMP is kept at the ground voltage Vss until VCCint increases to the voltage Vref . The driver 40 is then activated to transfer charge from the input node 3 to the output node 1. This causes the internal voltage VCCint to increase to the reference voltage Vref, and then the comparison result signal switches to the external voltage level. The driver 40 is then deactivated.
However, in the conventional internal power supply circuit described above, the internal voltage VCCint may rise momentarily, as shown by graph "A" of FIG. 7, due to noise or a short-circuit between internal circuit lines which receive voltages that are relatively high with respect to the internal voltage. This causes serious problems such as increased power consumption and changes in operational characteristics of internal circuits, for example, the trip points of inverters change.